The biggest thing with sleep training is being consistent, so if you want to do it, then you have to make sure to stick to it fully. It will take some time (a week at the most, but usually less) and she will get it. Also, if she is up longer in between, she will probably sleep longer.
As for size of food, it's the right size if it fits between your thumb and pointer finger. Shoving food in their mouths is normal, mine still does it. But they learn what is too much because they gag (also totally normal). When mine first started, I would only put 2 pieces on her tray at a time so she couldn't put so much in. Honestly, the gagging can be nerveracking, but it's a really important part of them learning to eat.